Why is this bone not pointing up / downwards?
Perhaps the designer of the armature .. or rig decided they needed a convenient handle on the armature. Like a coffee cup has a handle or that plastic attachment for cell phones is a handle. Bones can be used for many different things.  Blender Bones can be for human, monster, and other organic creatures.  Bones can control meshes that represent hard objects as well like a car.  You can change the appearance of bones.  The bones of an armature can have zero or some effect on the mesh.  They are flexible in their use. That bone may serve as a handle to indirectly control other bones which directly control mesh.  That control can be changed or deleted.  If the mesh has a vertex group that has the same names as a bone then it can have some effect.  If you decide to delete the vertex group then that connection will be destroyed. Weight painting can change the weights in a vertex group.
So parenting an armature to a mesh with automatic weights is just one use of armature bones.  Some time you might like to control many things at once and bones can do that as well since you might assign a hard object to each separate bone.